Teachers have vowed to press ahead with a one-day walkout in a bitter row over pay and conditions amid calls to halt the strike because it will disrupt children's education.

Tens of thousands of teachers are expected to take part in tomorrow's action, potentially forcing schools across England and Wales to close to some or all pupils.

The strike, which has been condemned by the Department for Education (DfE) has been called by the National Union of Teachers (NUT) as part of a dispute over changes to pay and working conditions as well as pensions.

Union leaders said that the national walkout was a "last resort" but would be going ahead.

As NUT members prepared to join picket lines, a spokesman for the Prime Minister said that David Cameron would urge them not to strike.

Mr Cameron's official spokesman told a Westminster media briefing: "He would call on them not to strike, because it disrupts children's education and children's families."

NUT deputy general secretary Kevin Courtney said: "It's still going ahead. Striking is our last resort. We have been trying to persuade Michael Gove to change his mind, he is unwilling. Michael Gove's policies are exhausting and demoralising teachers and that's very bad and disruptive for education.

"Thousands of good people are leaving the profession, we are building up to a teacher shortage and our children deserve energetic and enthusiastic teachers not demoralised and exhausted ones."

Mr Courtney added that the union wants the Education Secretary to change his policies on school accountability, which the NUT says is leading to "enormous" workloads for teachers, performance related pay and pensions.

A DfE spokesman said: "Parents will struggle to understand why the NUT is pressing ahead with strikes over the Government's measures to let heads pay good teachers more.

"They called for talks to avoid industrial action, we agreed to their request, and talks have been taking place weekly.

"Despite this constructive engagement with their concerns, the NUT is taking action that will disrupt parents' lives, hold back children's education and damage the reputation of the profession."

Mr Gove today wrote to seven union bosses, setting out the progress he believed had been made in an ongoing programme of talks between the DfE and these teaching unions.

In it, he said he wanted to underline his commitment to the talks process.

"I have been following the progress of the weekly talks closely and am encouraged by reports from the meetings so far," Mr Gove wrote.

"I hope you also feel that we are making good progress."

The NUT has been embroiled in its current dispute with the Government for more than two years, and staged a series of regional strikes with the NASUWT teaching union last year. Between them they represent the vast majority of teachers.

A proposed one-day national walkout in November by the two unions was called off and the NASUWT has decided not to take part in tomorrow's walkout.